Infection with the pathogenic fungus, Histoplasma capsulatum (Hc), produces a spectrum of illness ranging from acute pulmonary disease to chronic pulmonary infection to progressive disseminated histoplasmosis. In the vast majority of individuals, infection resolves without therapeutic intervention. Clearance of the organism is critically dependent on a collaboration between T cells and macrophages. It is presumed that upon recognition of antigen(s), Hc-reactive T cells release cytokines that activate macrophages to inhibit the intracellular growth of Hc. Two antigens, HIS-62 and HIS-80, have been shown to induce cellular immune responses in mice and mediate protection against Hc yeasts. Recently, the gene encoding HIS-62 has been cloned, sequenced and expressed and similar work on HIS-80 has begun. The overall objective of this proposal is to gain a better understanding of the interaction of T cells with Hc antigens. Since T cells ultimately respond to peptides, this proposal seeks to advance beyond the study of native HIS-62 and HIS- 80, and it will examine the immunobiological activity of peptides from these antigens. The specific aims are: 1) To clone, sequence and express HIS-80. Recombinant proteins will be tested for their capacity to induce cellular immune responses in mice and to confer protection in models of pulmonary and systemic histoplasmosis; 2) To analyze the antigenicity and immunogenicity of peptides from HIS-62 and HIS-80, and 3) To generate murine T cell clones reactive with peptides. The clones will be analyzed for a) T cell receptor expression by molecular genetic techniques, b) proliferative responses to peptides c) cytokine production, d) ability to modify Hc infection, e) induction delayed-type hypersensitivity responses, and f) major histocompatibility complex restriction of recognition. Thus, it may be possible to correlate the functional activity of T cells with their expression of specific T cell receptor family. Furthermore, HIS-62 and HIS-80 may serve as a paradigm for the interaction of Hc antigens with T cells.